USB: modifications for at91sam9g10

Modify both host and gadget USB drivers for at91sam9g10.
This add a clock management equivalent to at91sam9261 on usb drivers.
It also add the way of handling gadget pull-ups (like the at91sam9261).

Signed-off-by: Hong Xu <hong.xu@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>